The mammalian auditory cortex is comprised of several areas which can be distinguished on the basis of anatomical and physiological differences. The major objectives of the proposed research is to determine in greater detail the anatomical and physiological substrates which underly information processing in the auditory cortex of higher primates. Specific goals include: (1) description of the cortical, callosal, and thalamic connections of the three auditory cortical regions (core, belt, parabelt) and their respective subdivisions; (2) derivation of tonotopic/functional maps of each region and subdivision based on multi- unit responses to pure tone, bandpass noise bursts, and species-specific vocalizations; and (3) formulation of a basic theory of information processing within and between each auditory region. Microelectrode mapping, neuroanatomical tracing of connections, architectonic analysis, and standard histochemical staining methods will be used in combination to determine the borders between fields. Parallel experiments will be conducted in New World (owl) monkeys for technical advantages, and Old World (macaque) monkeys for their closer phylogenetic relationship to humans. The underlying premise is that the auditory system includes an array of control areas that are modularly organized and hierarchically interconnected, with parallel and serial components. The proposed studies will provide a better understanding of the anatomical and physiological substrates on which the processing and distribution of auditory information are based. This work will also serve as a framework for subsequent research on adult plasticity and recovery from peripheral or central auditory impairments.